JP4231329B2 - Molded body containing dried gel and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a shaped article containing dry gel and improved strength compared with conventional article. <P>SOLUTION: The method for producing a shaped article containing dry gel comprises a step to prepare dry gel powder containing &le;1 cm<SP>3</SP>/g of pores having a pore diameter of &ge;2 nm and &le;40 nm, a step to prepare a binder composition containing a binder and a solvent, and a step to shape the dry gel powder to a prescribed shape by using the binder composition. The process for producing the dry gel powder comprises a step to prepare the 1st gel having the 1st solid skeleton and the 1st fine pores and a reconstruction step to decompose at least a part of the 1st solid skeleton and construct the 2nd solid skeleton thicker than the 1st solid skeleton. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

【００８６】
一般にアルコキシシランを用いて形成されたゲルは、固体骨格を形成する粒子が小さく、粒子表面にあって重合に寄与していない官能基の数が多い。本実施形態の製造方法によると、再構築ゲル原料溶液中で形成された１０〜１００ｎｍの粒子が主として新たな骨格を形成する、すなわち第１ゲルの固体骨格の表面に結合するため、表面積が減少し、それに応じて表面に残された官能基も減少すると考えられる。本実施形態による乾燥ゲルをＳＥＭ観察すると、固体骨格の表面に１０ｎｍ程度から数十ｎｍの粒子の存在が確認できる。
【００８７】
また、再構築触媒と水の添加濃度により、室温以下でも再構築を十分に進行させることができるので、昇温を嫌う材料や部品等使う必要がある場合に、本実施形態の製造方法は特に好ましい。
【００８８】
また、再構築工程では、第１ゲル化で形成された湿潤ゲルの外部ではなく、湿潤ゲルの固体骨格上で選択的に進行することが重要である。そのためには、再構築ゲル原料が、第１湿潤ゲル内に十分に入って行くために、ゲル化に要する時間を長くすることが好ましい。あるいは、再構築ゲル原料が、短い時間で湿潤ゲル中に入って行くように、湿潤ゲルを小さな片あるいは粒子とするか、薄膜とすることが好ましい。
【００８９】
既に述べたように初期に低密度ゲル骨格を形成することで、ゲル化時の収縮が小さくなるため、収縮による割れや基体からの欠落が減少し、断熱材、吸音材、絶縁材料、音響整合層等として使用される時の良好な性能が確保され、特性のばらつきも小さくなるという効果を奏する。また、多孔体の細孔径も大きくなることから、事故などで有機溶媒に接触した際、乾燥過程に生じる割れや収縮が低減され、使用時の信頼性が高くなるという効果を奏する。
【００９０】
再構築工程で用いられる再構築触媒としては、第１ゲル化工程で用いられるゲル化触媒群の中のものを使用することができるが、特に、第１ゲル化工程時のゲル化触媒と同一のものである必要はない。
【００９１】
また、再構築工程で用いられる再構築ゲル原料としては、第１ゲル化工程で用いられるゲル原料が用いられ、第１ゲル原料と再構築ゲル原料との関係は、特に制限を受けない。例えば、第１ゲル化工程で、ゲル原料としてアルコキシシランであるテトラエトキシシランが用いられた場合には、再構築工程では、再構築ゲル原料としてテトラエトキシシランを用いることができる他、ゲル原料が溶解する溶媒を選べば、他の金属アルコキシドや、ケイ酸水溶液等も用いることも可能である。
【００９２】
この工程で用いられる溶媒は、上で述べたように再構築ゲル原料、再構築触媒が溶解すれば特に制限を受けない。
【００９３】
（疎水化工程）
再構築工程に続き、疎水化工程を実施する。この工程では、再構築工程までに得られた湿潤ゲルの表面に、溶媒中に溶解した疎水化剤を反応させることで、疎水基を導入する。疎水化剤は、後述するクロロシラン等の場合は、水と反応して湿潤ゲル表面との反応性が低下するため、疎水化の前に、水溶性の溶媒により洗浄することで、あるいは水と共沸する溶媒を用いて留去することで水を除くことが好ましい。
【００９４】
本発明に用いられる疎水化剤としては、反応性が高い点からシリル化剤が好ましく、例えばシラザン化合物、クロロシラン化合物、アルキルシラノール化合物およびアルキルアルコキシシラン化合物等がある。
【００９５】
これらのシリル化剤は、シラザン化合物、クロロシラン化合物、アルキルアルコキシシラン化合物の場合は、直接あるいは加水分解を受けて、対応するアルキルシラノールになってからゲル表面のシラノール基と反応する。また、アルキルシラノールをシリル化剤として用いれば、そのまま表面のシラノール基と反応する。
【００９６】
これらの中でも、疎水化時の反応性が高いことと入手の容易性から、クロロシラン化合物、シラザン化合物が特に好ましく、入手の容易性及び疎水化時に塩化水素、アンモニア等のガスを発生しないことからはアルキルアルコキシシランが特に好適に用いられる。
【００９７】
具体的には、トリメチルクロロシラン、メチルトリクロロシランおよびジメチルジクロロシランなどのクロロシラン化合物、ヘキサメチルジシラザンなどのシラザン化合物、メトキシトリメチルシラン、エトキシトリメチルシラン、ジメトキシジメチルシラン、ジメトキシジエチルシランおよびジエトキシジメチルシランなどのアルキルアルコキシシラン化合物、トリメチルシラノールおよびトリエチルシラノールなどのシラノール化合物に代表されるシリル化剤がある。これらを用いれば、湿潤ゲル表面にトリメチルシリル基などのアルキルシリル基を導入することで疎水化を進行させることができる。
【００９８】
また、疎水化剤として、フッ素化されたシリル化剤を用いれば、疎水性が強くなり非常に効果的である。
【００９９】
また、疎水化剤としては、エタノール、プロパノール、ブタノール、ヘキサノール、ヘプタノール、オクタノール、エチレングリコールおよびグリセロールなどのアルコール類の他、蟻酸、酢酸、プロピオン酸およびコハク酸などのカルボン酸なども用いることができる。これらは、ゲル表面の水酸基と反応してエーテルまたはエステルを形成することで疎水化を進めるが、反応が比較的遅いため高温の条件が必要である。
【０１００】
（乾燥工程）
疎水化工程に続き、乾燥工程を実施する。この工程では、疎水化工程までに得られた湿潤ゲルから溶媒を除くことにより、乾燥ゲルを得る。
【０１０１】
湿潤ゲルから溶媒を除く乾燥方法としては、（１）加熱乾燥法（２）超臨界乾燥法（３）凍結乾燥法の３つの方法がある。加熱乾燥法は、最も一般的簡便な乾燥法であり、溶媒を含む湿潤ゲルを加熱することで、液体状態の溶媒を気化させて除去するものであり、この乾燥によることが最も好ましい。なお、ここでいう「加熱乾燥」は、上記の加熱の程度が極端に低い場合として、加熱を行わずに放置して乾燥する自然乾燥も含むものとする。
【０１０２】
乾燥時に、ゲルの密度が低い場合にはゲル中の溶媒の表面張力に比例する毛管力のために、ゲルが一時的に収縮し割れを生じることがある。このため、乾燥時の溶媒は沸点での表面張力が小さい炭化水素系の溶媒が好ましく、特に安価なヘキサン、ペンタンあるいはその混合物が好ましい。一方、安全性の観点からは、イソプロパノール、エタノール、ブタノール等のアルコール類、さらに水あるいは水と有機溶媒との混合溶媒からの乾燥が好ましい。本実施の形態では湿潤ゲルが、後述の超臨界乾燥法により細孔容積が０．５ｃｍ³／ｇ以下、比表面積が３００ｍ²／ｇ以下の乾燥ゲルを与える湿潤ゲルであれば、アルコール類、水をはじめとする多くの溶媒からの乾燥によっても割れ、収縮が抑制される。
【０１０３】
超臨界乾燥法は、溶媒除去時の溶媒の表面張力を下げるために、表面張力が０である超臨界流体を用いるものである。乾燥時に、溶媒は液体状態を経ずに取り除かれる。乾燥に用いられる超臨界流体として、水、アルコール、二酸化炭素等の超臨界状態があるが、最も低温で超臨界状態が得られ、しかも無害である二酸化炭素が好適に用いられる。
【０１０４】
具体的には、まず耐圧容器中に液化二酸化炭素を導入することで、耐圧容器中の湿潤ゲル中の溶媒を液化二酸化炭素に置換する。次に、圧力と温度を臨界点以上に上げることで超臨界状態とし、温度を保ったまま徐々に二酸化炭素を放出して乾燥を完了させる。
【０１０５】
凍結乾燥法は、湿潤ゲル中の溶媒を凍結させた後に、昇華により溶媒を除く乾燥方法である。液体状態を経ず、ゲル中に気液界面を生じず毛管力が働かないために乾燥時のゲルの収縮を抑制することができる。
【０１０６】
凍結乾燥法に用いられる溶媒は、凝固点での蒸気圧が高いものが好ましく、第３ブタノール、グリセリン、シクロヘキサン、シクロヘキサノール、パラ−キシレン、ベンゼン、フェノールなどが挙げられる。これらのなかでも、融点における蒸気圧が高いという点から、特に第３ブタノール、シクロヘキサンが好ましい。
【０１０７】
凍結乾燥時には、湿潤ゲル中の溶媒を、上記の凝固点での蒸気圧が高い溶媒に置換しておくことが効果的である。また、ゲル化時に用いる溶媒を、凝固点での蒸気圧が高い溶媒にしておけば、溶媒置換を省略して効率的な製造が可能となるためより好ましい。
【０１０８】
乾燥は、疎水化工程の後に行ってもよいし、疎水化工程の前に行ってもよい。乾燥工程を経た後で疎水化する場合は、乾燥ゲルを溶液中ではなく、疎水化剤の蒸気にさらすことで乾燥ゲル表面に疎水基を導入する。従って、使用する溶媒量が減少するという効果を奏する。
【０１０９】
この時使用する、疎水化剤としては、上述の疎水化剤を用いることができるが、反応性の高さからトリメチルクロロシラン、ジメチルジクロロシラン等のクロロシラン化合物が最も好ましい。また、クロロシラン化合物以外の疎水化剤を用いる場合は、アンモニアや塩化水素等の気体状態で導入可能な触媒を用いることも有効である。
【０１１０】
また、気相で疎水化を行う場合は、溶媒や疎水化剤の沸点に制限を受けずに疎水化時の温度を高めることができる。従って、気相での疎水化は、反応を早めるために有効である。また、湿潤ゲルが薄膜や粉体であれば、疎水化剤蒸気の浸入が容易であり、薄膜の場合は溶媒量削減の効果も大きいためより好ましい。
【０１１１】
また、再構築工程と疎水化工程とを同時に行うことも可能である。この場合二つの工程を同時に進めるために、短時間で乾燥ゲルからなる多孔体が得られるという効果が得られる。
【０１１２】
再構築工程兼疎水化工程は、具体的には、第１ゲル化工程で得られた湿潤ゲルを、再構築工程で用いる再構築ゲル原料溶液と疎水化剤とを混合した処理液に浸漬することで実施する。こうすることで、ゲルの再構築と疎水化が同時に進行する。再構築原料、疎水化時の疎水化剤は、上述のものと同じものを用いることが可能である。例えば、水ガラスから電気透析により得られるケイ酸水溶液から第１ゲル化を行った後、得られた湿潤ゲルを、水溶性溶媒を用いること等により、ゲル原料であるアルコキシシランと、疎水化剤であるシラザン化合物等とを溶解させた溶液中で、再構築と疎水化とが同時に行われる。
【０１１３】
上記のように再構築工程と疎水化工程とを同時に行う場合、溶解性等を満たせば特にこれらのゲル原料や疎水化剤の組み合わせに制限されるものではない。また、疎水化剤として、アルキル基を有する、多官能のアルキルアルコキシシラン、クロロシラン、アルキルシラノールを用いると、アルキル基がゲル骨格の中に導入されるため、ゲルに柔軟性が付与され、脆さが改善されるという効果も奏する。このとき、ゲル骨格の中心部は堅く、周辺部は柔軟性を有した特徴的な構造を有することになる。
【０１１４】
上述のようにして、固体骨格の表面が疎水性を有する乾燥ゲルを得ることができる。また、上述の製造プロセスにおいて、疎水化工程を省略することによって、固体骨格の表面が親水性を有する乾燥ゲルを得ることができる。再構築工程を経た湿潤ゲルは微細な細孔が減少し、且つ固体骨格が太くなっているので、表面が親水性のままで乾燥処理（加熱乾燥を含む）を行っても、ゲルの収縮や割れの発生が抑制される。例えば、金属酸化物で固体骨格を形成する場合、固体骨格の表面が親水性の良好な乾燥ゲルを得ることができる。
【０１１５】
（粉砕工程）
上述のようにして得られた乾燥ゲルを公知の方法で粉砕することによって、乾燥ゲル粉末を得る。粉砕は、例えば、ブレンダー（例えば、ウォーリング社製、７００Ｓ型）を用いて実行される。乾燥ゲル粉末の粒径は、特に限定されず、数十ミクロンメーターオーダー以下の粉末であってもよい。粉砕の容易性の観点からは、１μｍ以上１００μｍ以下の範囲の乾燥粉末を用いることが好ましい。また、粒径の分布は幅が広い方が充填性が向上するので好ましい。
【０１１６】
また、粉砕工程は、第１ゲル化工程から乾燥工程までの間に行っても良い。他例えば、第１湿潤ゲルを作製しながら、あるいは、第１湿潤ゲルが作製された後、その溶液中で撹拌等によって第１湿潤ゲルを粉砕しても良い。このように、第１湿潤ゲルの段階で粉砕しておくと、後の再構築工程および／または乾燥工程における処理効率が向上するという利点が得られる。また、第１ゲル原料溶液を貧溶媒中に分散した状態で、第１ゲル化工程を行うことによって、粒子上の湿潤ゲルを得ることもできる。
【０１１７】
（バインダ組成物）
乾燥ゲル粉末の溶媒親和性（親水性または疎水性）によって、および／または成形体の用途によって、バインダ組成物（バインダおよび溶媒）を選択する。上記の乾燥ゲルは耐溶媒性に優れるので、種々のバインダ組成物を用いることができる。
【０１１８】
バインダ組成物と乾燥ゲル粉末とを混合して成形用の組成物を得る方法は、公知の方法で実行できる。例えば、乳鉢やボールミル、ホモジナイザーなどを用いて混合することができる。
【０１１９】
また、成形用の組成物中に補強材を混合してもよい。あるいは、補強材中に上記成形用組成物を流し込んで、補強材を含有した成形体を形成することもできる。好適に用いられる補強材としては、ハニカム構造体や、ガラス繊維もしくは鉱物繊維、有機繊維（例えば、ポリエステル系繊維、アラミド系繊維、ナイロン系繊維等の合成繊維の他に天然繊維）あるいは、これらの繊維からなる繊維布や不織布等の繊維集合体も使用することができる。また、ポリウレタン系、ポリエステル系、塩化ビニル系、ポリオレフィン系、ポリスチレン系、シリコーン系等のフォームも用いることができる。
【０１２０】
また、成形体の表面に保護膜を形成してもよい。保護膜を形成することにより、表面の強度が上昇し、取り扱いがより容易になる効果がある。
【０１２１】
（疎水性乾燥ゲル粉末を含む成形体）
疎水性を有する乾燥ゲル粉末と疎水性のバインダ組成物とを用いて成形体を作製する実施形態を説明する。ここで言う疎水性を有する乾燥ゲル粉末とは、乾燥ゲル粉末を水と混ぜたときに、乾燥ゲル粉末が水に浮き、細孔内部に水が実質的に浸入しない乾燥ゲル粉末のことを意味する。このような疎水性は、上記の疎水化工程を行うことによって付与され、無機酸化物系の乾燥ゲルであれば容易に疎水性を付与することが可能である。また、有機系のゲルでも、上述した疎水化剤と反応するものであれば疎水性を付与することができる。
【０１２２】
乾燥ゲル粉末が疎水性を有している場合、従来の成形法では、ゲルの細孔内に成形用の組成物中の有機溶媒が浸入、乾燥する際に、ゲルの収縮が起こり、成形体の密度が上昇する。これに対し、本実施の形態では、２ｎｍ以上４０ｎｍ以下の細孔に対応する細孔容積が１．０ｃｍ³／ｇ以下と小さい乾燥ゲル粉末を用いることによって、細孔径に比例する毛管力が低減され、ゲルの収縮が抑制される。
【０１２３】
バインダとしては、有機溶媒に溶解するものであれば使用することができる。上述したように、ケイ素樹脂系、アクリル樹脂系、ビニル樹脂系、酢酸ビニル樹脂系、フェノール樹脂系、セルロース系等の一般的なバインダが使用可能である。
【０１２４】
また、従来の疎水性乾燥ゲルを用いた場合、ゲルが疎水性を有しているため細孔内に水は侵入しないが、有機溶媒と水との混合溶媒がゲルの細孔内に侵入することがある。水を含有した溶媒が細孔中で気液界面を生じる場合に発生する毛管力は大きく、従来の乾燥ゲルからなる成形体では収縮が顕著であるが、本発明の実施形態の乾燥ゲルを用いるとこのような場合においても成形体の収縮が抑制される。
【０１２５】
（親水性乾燥ゲル粉末を含む成形体）
親水性を有する乾燥ゲル粉末と親水性のバインダ組成物とを用いて成形体を作製する実施形態を説明する。ここで言う親水性を有する乾燥ゲル粉末とは、水中に乾燥ゲル粉末を投じたときに、水を吸収する乾燥ゲル粉末を指す。
【０１２６】
乾燥ゲル粉末が親水性を有している場合、従来の成形法では、ゲルの細孔内に成形用の組成物中の水や有機溶媒が浸入し、この侵入の際および乾燥する際に、ゲルの収縮が起こり、成形体の密度が上昇する。本実施の形態では、２ｎｍ以上４０ｎｍ以下の細孔に対応する細孔容積が１．０ｃｍ³／ｇ以下と小さい乾燥ゲル粉末を用いることによって、溶媒中に水が含まれる場合でも、細孔径に比例する毛管力が低減されてゲルの収縮が抑制される。
【０１２７】
また、従来の乾燥ゲルからなる成形体の製造方法では、低密度の成形体を得るためには、ゲル中への溶媒の浸入を防ぐことが必要であり、そのためには疎水性の乾燥ゲルと水系の溶媒を用いたバインダを組み合わせるしかなかった。乾燥ゲルが疎水性を有する場合は、ゲル表面には、低エネルギーの表面を形成するアルキル基などの疎水性の有機基によって覆われているため、バインダの持つ極性基との間の引力的な相互作用弱く、バインダによる結合力（接着力）が低下する。
【０１２８】
それに対し、本実施形態のように、乾燥ゲル粉末が親水性を有する場合は、バインダの持つ極性基との間に引力的な相互作用が強く働くため、バインダによる結合力が強くなる効果がある。さらに、乾燥ゲルの固体骨格の表面にある極性基が、バインダの持つ極性基と反応して結合を形成する場合は、より強度の高い成形体が得られる。例えば、乾燥ゲル粉末の表面に水酸基が存在し、親水性を示している場合、例えば、バインダの持つイソシアネート基、水酸基、エポキシ基、カルボキシル基、メトキシメチル基等と反応することによって、ウレタン結合、エーテル結合、エステル結合、メチレン結合を形成する。
【０１２９】
本実施形態で用いられるバインダとしては、上述したものを用いることができるが、特に水酸基等の極性基を有するバインダが好ましい。
【０１３０】
本実施形態で使用される乾燥ゲル粉末としては、親水性を有していれば有機、無機にかかわらず、上述の乾燥ゲル粉末を用いることができる。特に、酸化ケイ素等からなる金属酸化物系の乾燥ゲル粉末の場合、表面に多数の水酸基を有しているため、好適に使用できる。また上記金属酸化物系の乾燥ゲルの場合、バインダは、上述の様にイソシアネート基、水酸基、エポキシ基、カルボキシル基、メトキシメチル基を持つものの他に、シラノール基あるいは、加水分解等によってシラノール基を生じる、シラノール系、アルコキシシラン系のバインダを用いれば、シラノール基の縮合による結合の形成が容易であるため好ましい。
【０１３１】
また、既に述べたように、親水性を有する乾燥ゲル粉末を成形した後に、残存している水酸基に対して、疎水化剤を気相で作用させることで反応させて、疎水性を付与することも可能である。
【０１３２】
以下に、具体的な実施例に基づいて本発明を説明するが、本発明は、以下で用いた特定のゲル原料、ゲル化触媒等の原材料の種類、溶媒、バインダ等の内容に必ずしも制限されるものではない。
【０１３３】
【実施例】
《実施例１および比較例１》
本実施例では、疎水化した乾燥ゲル粉末と有機溶剤およびバインダとを混合した成形用組成物を作製し、これを用いて成形体を作製した。
【０１３４】
（１）第１ゲル化工程
まず、テトラエトキシシラン／エタノール／水／塩化水素＝１／１５／１／０．０００７８（モル比）で混合して、６５℃の恒温槽に３時間に置くことにより、テトラエトキシシランの加水分解を進行させた。次に、さらに、水／ＮＨ₃＝２．５／０．００５７（テトラエトキシシランに対するモル比）を加えて混合し、１日間５０℃恒温槽中に置き、ゲル化を進行させ、湿潤ゲルを得た。この時点で、湿潤ゲルを切断し、１０ｍｍ×１０ｍｍ×３ｍｍの形状とした。
【０１３５】
（２）再構築工程
再構築原料（第２ゲル原料）としてテトラエトキシシラン、再構築触媒（第２触媒）としてアンモニア水を用いた。ゲル化第１工程で得られた湿潤ゲルを、テトラエトキシシラン／エタノール／アンモニア水＝６０／３５／５（体積比）で混合して得られる再構築原料溶液（第２ゲル原料溶液）に浸積して７０℃恒温槽中で処理を行った。処理時間は、９時間、１０．５時間、１３時間、２４時間の３つの場合を別々に行った。アンモニア水は０．１Ｎのものを用い、第２ゲル原料溶液は、湿潤ゲル体積の２０倍量を使用した。
【０１３６】
（３）疎水化工程
再構築工程で得られた湿潤ゲルを、ゲル体積の５倍体積のイソプロピルアルコールに浸漬して２回洗浄を行った。この湿潤ゲルを、ジメチルジメトキシシラン／イソプロピルアルコール／アンモニア水＝４５／４５／１０（重量比）を混合して得られる疎水化液に４０℃で１日間、混合しながら疎水化処理を行った。疎水化液としては、湿潤ゲルの体積の２０倍量を使用した。
【０１３７】
（４）乾燥工程
最後に、疎水化されたゲルを、ゲル体積の５倍体積のイソプロピルアルコールに浸漬して２回洗浄を行った。次に、ゲルを耐圧容器の中に入れ、この容器中に液化二酸化炭素を流通させることで、ゲル内のイソプロピルアルコールを液化二酸化炭素に置換した。次に、容器内にさらに液化二酸化炭素をポンプで送り込むことにより、容器内の圧力を１０ＭＰａまで上昇させた。その後、５０℃まで昇温することで容器内を超臨界状態とした。次に、温度を５０℃に保ったまま、圧力をゆっくりと開放することで乾燥を完了した。
【０１３８】
（５）粉砕工程
得られた乾燥ゲルをブレンダー（ウォーリング社製）を用いて粉砕して粉末とした。得られた乾燥ゲル粉末の平均粒径は、２５μｍであった。
【０１３９】
得られた乾燥ゲルの密度、２ｎｍ以上４０ｎｍ以下の細孔に対応する細孔容積、比表面積を測定した。密度は、重量測定と、乾燥ゲルを水に浸漬した際の浮力から体積を求めて、この値から算出した。細孔容積および比表面積は、窒素吸着法によりＢＪＨ法、ＢＥＴ法を適用して算出した。
【０１４０】
再構築工程の処理時間が、９時間、１３時間、２４時間の順に、密度（１５０ｋｇ／ｍ³、２５０ｋｇ／ｍ³、４２０ｋｇ／ｍ³）、細孔容積（０．９ｃｍ³／ｇ、０．５ｃｍ³／ｇ、０．３ｃｍ³／ｇ）、比表面積（３９０ｍ²／ｇ、２７０ｍ²／ｇ、１８０ｍ²／ｇ）であった。
【０１４１】
（６）成形体の作製
上記のプロセスで得られた乾燥ゲル粉末１００ｇと、バインダとしてＮ−メトキシメチルポリアミドであるファインレジンＦＲ−１０１（（株）鉛市製）１５ｇおよびメタノール２００ｇ、マレイン酸０．２ｇとを乳鉢を用いて混合して、スラリー状の成形用組成物を作製した。
【０１４２】
この組成物の１部を、底面が３ｃｍ×３ｃｍの型に流し込み、５０℃でメタノールを蒸発させて乾燥し、さらに、１２０℃で１時間加熱することで、上記のメトキシメチル基とアミド基との水素との間で脱メタノール反応により架橋を形成して成形体を形成した。
【０１４３】
得られた成形体の密度を、その質量と、形状から決まる体積とから算出した。算出された密度は、再構築工程の時間が、９時間、１３時間、２４時間のものが、順に１４０ｋｇ／ｍ³、２２０ｋｇ／ｍ³、３６０ｋｇ／ｍ³であった。
【０１４４】
（比較例１）
比較のために、テトラエトキシシラン／エタノール／水＝１／１／４（モル比）を混合して室温にてゲル化を進行させた。水は０．１Ｎアンモニア水の形で添加混合した。その後、実施例１と同様にして疎水化、乾燥を行った後に、粉砕して乾燥ゲル粉末を得た。但し、乾燥時には、ゲルの収縮を押さえるために、イソプロピルアルコールではなく、ゲル内の溶媒をヘキサンに置換した後、乾燥を行った。得られた乾燥ゲル粉末の密度は２９０ｋｇ／ｍ³であった。
【０１４５】
この乾燥ゲル粉末を用いて、実施例１と同様に、成形体を作製した。得られた成形体の密度は、４８０ｋｇ／ｍ³であった。
【０１４６】
このように、実施例１では、比較例１に比べて、使用した乾燥ゲル粉末の密度が高い場合でも、成形体の密度は、低いものが得られた。これは、比較例１では、乾燥ゲル粉末が持つ微細な細孔のために、細孔に侵入した溶媒が乾燥工程において除去される際にゲルの収縮が進行したのに対し、実施例１では、乾燥ゲル粉末が微細な細孔を僅かしか有しなしため、乾燥時の収縮が抑制されたためと考えられる。
【０１４７】
《実施例２および比較例２》
本実施例では、疎水化された乾燥ゲルと溶媒としての水、バインダとしてフェノール樹脂とを混合して、成形用組成物を作製し、これを用いて成形体を作製した。
【０１４８】
実施例１において作製した、再構築工程の処理時間が２４時間の乾燥ゲル粉末１００ｇと、バインダとしてフェノール樹脂であるフェノライトＰＧ−５８０（大日本インキ化学工業（株））３０ｇと、水２００ｇとを乳鉢を用いて混合して、スラリー状の成形用組成物を作製した。
【０１４９】
この組成物の１部を、底面が３ｃｍ×３ｃｍの型に流し込み、８０℃で水を蒸発させて乾燥し、さらに、１５０℃で２時間加熱することで、架橋促進して成形体を形成した。
【０１５０】
得られた成形体の密度は、３８０ｋｇ／ｍ³であった。
【０１５１】
（比較例２）
乾燥ゲル粉末として、テトラエトキシシラン／エタノール／水＝１／３／４（モル比）を用いて湿潤ゲルを作製した以外は、比較例１と同様にして乾燥ゲル粉末を得た。乾燥ゲルの密度は、２１０ｋｇ／ｍ³であった。
【０１５２】
上記の乾燥ゲル粉末を用いて、実施例２と同様にして、成形体を作製した。得られた、成形体の密度は、６２０ｋｇ／ｍ³であった。
【０１５３】
このように、実施例２では、比較例２に比べて、使用した乾燥ゲルの密度が高いにもかかわらず、成形体の密度は低くなった。これは、比較例２では、乾燥ゲル粉末が有する微細な細孔に表面張力が大きい水が浸入することにより、より大きな毛管力が生じて、乾燥ゲルの収縮が進行したのに対し、実施例２では、乾燥ゲル粉末が微細細孔を僅かしか有しないため、収縮が抑制されたためと考えられる。
【０１５４】
《実施例３および比較例３》
本実施例では、親水性を有する乾燥ゲル粉末と有機溶剤およびバインダとを混合した成形用組成物を作製し、これを用いて成形体を作製した。
【０１５５】
実施例１のプロセスにおいて、再構築工程の処理を２４時間行った後、疎水化工程を省略して、乾燥を行うことで得られた乾燥ゲル粉末を用いた他は、実施例１と同様にして成形体を得た。
【０１５６】
上記の乾燥ゲル粉末および成形体の密度を、質量の測定と、形状から体積を求めることにより算出した。乾燥ゲル粉末の密度は、３９０ｋｇ／ｍ³、成形体の密度は、３６０ｋｇ／ｍ³であった。
【０１５７】
（比較例３）
比較例２と同様にして、乾燥ゲル粉末を作製した。但し、乾燥工程は、ゲル内の溶媒をエタノールに置換して自然乾燥することによって行った。こうして得られた乾燥ゲル粉末の密度は３７０ｋｇ／ｍ³であった。
【０１５８】
この乾燥ゲル粉末１００ｇと、シリコーン系界面活性剤ＴＳＤ−４５２２（東芝シリコーン社製）３ｇおよびバインダとして界面活性剤含有ウレタン系エマルジョン（ゼネカ社製、ＲＵ―４０―５７０）を固形分として、乾燥ゲル粉末の質量の１５％となるように混合してスラリー状の成形用組成物を作製した。
【０１５９】
この組成物を用いて、実施例３と同様にして成形体を得た。但し、成形に際しては、８０℃で水を蒸発させて乾燥を行った後、９０℃にて１日間放置することで成形を行った。得られた、成形体の密度は３９０ｋｇ／ｍ³であった。
【０１６０】
また、実施例３と比較例３で得られた成形体とを互いに重ねて、両側から圧力をかけたところ、比較例３の成形体が先に変形、割れを生じた。また、両方の成形体を水に浸漬し乾燥したところ、実施例３の成形体には密度変化がなかったが、比較例３の成形体では、２割以上の密度上昇が起こった。
【０１６１】
このように、実施例３の成形体の強度が高いのは、乾燥ゲル粉末の外部をバインダが覆い、且つ細孔の内部にバインダが侵入していることにより、乾燥ゲル粒子間の結合および乾燥ゲル粉末そのものの強度が増大しているのに加え、乾燥ゲル粉末の固体骨格表面の水酸基とバインダの持つメチロール基との間で縮合が起こり、強固な結合が実現されているためと考えられる。
【０１６２】
【発明の効果】
本発明によると、従来よりも強度が向上した、乾燥ゲルを含む成形体およびその製造方法が提供される。
【０１６３】
本発明の成形体は、細孔径が２ｎｍ以上４０ｎｍ以下の範囲の細孔の容積が１ｃｍ³／ｇ以下である乾燥ゲル粉末を含むので、溶媒やバインダが細孔に侵入しても、ゲルの収縮や割れが発生しないので、強度の高い成形体を得ることができる。
【０１６４】
本発明によると、疎水性を有する乾燥ゲル粉末を用いても、親水性を有する乾燥ゲル粉末を用いても、従来よりも低密度の成形体を得ることができる。
【０１６５】
本発明による成形体は、低密度で従来よりも強度が高く、さらに、使用時の耐溶剤性も優れている。従って、本発明による成形体は、断熱材や音響整合層等に好適に適用され、使用環境の制限が大幅に緩和されるという効果を奏する。
【図面の簡単な説明】
【図１】本発明による実施形態の乾燥ゲルの製造方法を説明するための模式図である。
【図２】（ａ）本発明による実施形態の乾燥ゲルの製造方法における第１固体骨格を模式的に示す図であり、（ｂ）は再構築工程を経て得られた第２個体骨格を模式的に示す図である。
【図３】（ａ）〜（ｅ）は、再構築原料溶液（実施例１）に生成される粒子の粒度分布を測定した結果を示すグラフである。
【図４】（ａ）は、種々の乾燥ゲルについてＢＪＨ法によって求めた累積細孔曲線（細孔容積（ｃｍ³／ｇ）と細孔径（細孔直径）との関係）を示すグラフであり、（ｂ）は微分細孔曲線である。
【符号の説明】
１ 第１ゲル原料溶液
２ 第１湿潤ゲル
３ 再構築原料溶液（第２ゲル原料溶液）
４ 第２湿潤ゲル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a molded article including a low-density dry gel used for a heat insulating material, a sound absorbing material, a catalyst carrier, an insulating material, an acoustic matching layer of a transducer such as an ultrasonic wave, and a manufacturing method thereof.
[0002]
[Prior art]
A dry gel is obtained by mixing a gel raw material, water, a solvent, and a gelation catalyst to form a wet gel, and then removing the solvent by drying. However, during drying, the gel contracts due to the capillary force generated in the pores. At this time, the contracted state is fixed by bonding of hydroxyl groups present in the pores of the gel.
[0003]
In order to prevent this, the contact angle θ of the solid-liquid interface is increased by modifying the surface of the wet gel with an organic silyl group to make it hydrophobic, which is proportional to γ cos θ (γ is the surface tension of the liquid in the wet gel). A method for reducing the capillary force is disclosed in Non-Patent Document 1, for example.
[0004]
According to Non-Patent Document 1, a wet gel is formed by a sol-gel method using an alkoxysilane that is a metal alkoxide as a gel raw material, and water remaining in the wet gel is removed by alcohol substitution. Subsequently, the hydrophobization is carried out by introducing an organic silyl group on the surface of the gel by allowing a silylating agent to act on the surface of the wet gel in a hydrocarbon solvent. Drying is performed by removing the hydrocarbon solvent in the wet gel by heat drying. According to the above method, since the hydroxyl group is decreased, the contracted state is not fixed.
[0005]
On the other hand, Patent Document 1 discloses that an alcogel is formed by hydrolysis and polycondensation of tetraalkoxylane, and the resulting alcogel is brought into contact with a solution of tetraalkoxysilane, whereby the skeleton of the alcogel (solid skeleton) can be strengthened. Are listed.
[0006]
The porous body made of the low-density dry gel obtained as described above has a low density, a large specific surface area, a fine pore structure, a low dielectric constant, and a low acoustic impedance, so that a heat insulating material, a sound absorbing material, and a catalyst carrier. It is used for interlayer insulating materials such as LSIs, acoustic matching layers of ultrasonic transducers, and the like.
[0007]
For example, as a heat insulating material, solid heat conduction is reduced because of its low density. In addition, since it has a finer pore structure, it exhibits excellent heat insulation performance. Moreover, higher heat insulation performance is exhibited by containing it in a decompressed container. This heat insulating material is used, for example, for heat insulation of a thermal home appliance or a house.
[0008]
When used for the above-mentioned heat insulating material and other applications, as a form of use, it is used by filling a container or the like as a dry gel powder. Furthermore, it is preferable in terms of handling that the powder is molded with a binder. In the present specification, “powder” broadly includes those composed of particles and / or granules. Unless otherwise specified, the term “particle” is used as a term representing a constituent element of a powder and includes “granule”.
[0009]
As the binder, a solid binder or a liquid binder is used. When a solid binder such as a hot melt adhesive is used as the binder, it is difficult to uniformly cover the surfaces of the individual particles constituting the dry gel powder and bond the particles to each other. For this reason, generally, if the amount of the binder component (solid content) excluding the solvent is the same, the liquid binder (binder composition) exhibits a stronger binding force than the solid binder. In the present specification, a material containing a binder and a solvent may be referred to as a “binder composition”.
[0010]
The liquid binder composition can be obtained by dissolving a solid or liquid binder in an organic solvent or water, or by forming an aqueous emulsion or the like. When this liquid binder composition is used, when the dried gel powder has an affinity for a solvent (water or an organic solvent), the solvent penetrates into the pores of the dried gel powder. In this case, as already described, when the solvent enters and is dried, the gel contracts due to the capillary force caused by the gas-liquid interface formed in the pores of the gel. Therefore, it is difficult to obtain a low-density molded body by binding a low-density dry gel powder having a high affinity for a solvent with a liquid binder.
[0011]
In order to suppress the penetration of this solvent, for example, when the dried gel powder has hydrophobicity, it is preferable to use water as the solvent. Specifically, it is preferable to use an aqueous solution of a water-soluble polymer or an aqueous emulsion of a water-insoluble polymer as the binder in a liquid state. Patent Document 2 discloses that a surfactant is used to improve the wettability between the surface of the hydrophobic dry gel particles and the binder, but the strength of the resulting molded product is not sufficient.
[0012]
[Patent Document 1]
JP-T 6-510268
[Patent Document 2]
Japanese Patent Laid-Open No. 10-147664
[Patent Document 3]
Japanese Unexamined Patent Publication No. 2000-012313 (especially Example 1 and Example 2 in Table 1)
[Patent Document 4]
Japanese Patent No. 3243107 (especially Table 1)
[Non-Patent Document 1]
Journal of Crystalline Solid 186, 104-112, 1995.
[0013]
[Problems to be solved by the invention]
As described above, in the conventional manufacturing method, the low density (particularly the density is 500 kg / m 2). ^Three There was a problem that the strength of the molded product obtained by bonding the dry gel of the following) with a binder was weak. That is, when a solvent or a binder enters into the pores of the dried gel, shrinkage or cracking of the dried gel occurs, and it is necessary to suppress this.
[0014]
This invention is made | formed in view of said various points, The main objective is to improve the intensity | strength of the molded object containing a dry gel with low density.
[0015]
[Means for Solving the Problems]
The method for producing a molded product of the present invention is a method for producing a molded product containing a dry gel, wherein the pore volume in the range of the pore diameter of 2 nm to 40 nm is 1 cm. ^Three Including a step of preparing a dry gel powder that is less than / g, a step of preparing a binder composition containing a binder and a solvent, and a step of forming the dry gel powder into a predetermined shape using the binder composition In this way, the above object is achieved.
[0016]
In one embodiment, the method includes a step of allowing the binder to enter into pores of the dry gel powder.
[0017]
In one embodiment, the dry gel powder is hydrophobic and the solvent is an organic solvent.
[0018]
In one embodiment, the dry gel powder has hydrophilicity.
[0019]
In one embodiment, the solid skeleton of the dry gel powder is formed from an inorganic material.
[0020]
In one embodiment, the inorganic material includes silicon oxide.
[0021]
In one embodiment, the step of producing the dry gel powder includes preparing a first gel having a first solid skeleton and first pores, decomposing at least a part of the first solid skeleton, and A restructuring step of forming a second solid skeleton thicker than the first solid skeleton, a step of obtaining a dry gel by drying the gel obtained by the restructuring step, and a step of pulverizing the dry gel Include.
[0022]
The molded body of the present invention is a molded body including a dry gel powder and a binder, and the pore volume of the dry gel powder having a pore diameter in the range of 2 nm to 40 nm is 1 cm. ^Three / G or less.
[0023]
It is preferable that the binder penetrates into the pores of the dry gel powder.
[0024]
The composition of the present invention is a composition comprising a dry gel powder, a binder, and a solvent, wherein the dry gel powder has a pore volume of 1 cm in a pore diameter range of 2 nm to 40 nm. ^Three / G or less.
[0025]
It is preferable that the solvent penetrates into the pores of the dry gel powder.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Below, the molded object containing the dry gel of embodiment by this invention and its manufacturing method are demonstrated.
[0027]
The molded body containing the dried gel of the embodiment according to the present invention has a pore volume of 1 cm in a pore diameter range of 2 nm to 40 nm. ^Three / G or less of dry gel powder and binder.
[0028]
As a result of the study of the present invention, the pore volume with a pore diameter in the range of 2 nm to 40 nm is 1 cm. ^Three The dry gel powder of less than / g is suppressed from shrinkage and cracking due to capillary force even if the solvent enters the pores (this property is sometimes referred to as “solvent resistance”). This effect is particularly noticeable for low density dry gels. This is because, despite the low density and weak strength, there are fewer fine pores than the conventional dry gel, and the capillary force proportional to the pore diameter can be reduced. Specifically, for example, the density is 200 kg / m. ^Three In the case of a low-density dry gel of the order, the pore volume of 2 nm to 40 nm is 2.5 cm in the conventional one ^Three / G but about 1 cm for the dry gel used in the present invention. ^Three / G or less. The dry gel powder has a density of 50 kg / m. ^Three 500 kg / m or more ^Three The pore volume between 2 nm and 40 nm is 0.5 cm. ^Three / G or less is particularly preferable.
[0029]
When dry gel powder with a small fine pore volume as described above is used, there is no deterioration in properties due to shrinkage or cracking of the dry gel even if a solvent or binder enters the pores. A molded body having high strength can be obtained. That is, in the conventional low-density dry gel, it was necessary to prevent the solvent and binder from entering the pores. However, when the above-mentioned dry gel is used, the binder is actively infiltrated into the pores, Strength can be improved. The factors that improve the strength of the compact are the improvement in strength as a bulk of the compact by spreading the binder to every corner of the compact and the strength of the gel particles by the penetration of the binder into the pores of the dried gel. There is an improvement.
[0030]
In addition, the above-mentioned dry gel powder has excellent solvent resistance not only to hydrocarbon-based hydrophobic solvents but also to hydrophilic solvents typified by water, so a liquid binder composition containing various solvents Can be used.
[0031]
In addition, since the surface of the solid skeleton of the dried gel powder is not only hydrophobic but also hydrophilic, it can be appropriately selected according to the type of solvent. That is, conventionally, the surface of the solid skeleton of the gel is made hydrophobic in order to suppress the shrinkage of the gel during drying, and the hydrophilic binder composition (aqueous system) is used to prevent the solvent from entering the pores. However, according to the present invention, there are no such restrictions, and various combinations are possible.
[0032]
The particle size of the dry gel powder is not particularly limited, and may be a powder of the order of several tens of micrometers. The material is not particularly limited, and an inorganic gel or an organic gel is used. Organic materials include phenolic, melamine and amide. In addition, various inorganic oxides can be used as long as they are inorganic materials, and there are oxides such as titanium, silicon, vanadium, aluminum, and zirconium.
[0033]
Among these, it is preferable that the main component of the dry gel is silicon oxide. This is due to the following reason. As described later in the production method, silicon oxide is obtained from an inexpensive water glass-based gel raw material, so that the production cost is reduced. In addition, since the alkoxide of silicon is milder in reactivity than other metal alkoxides, the reaction can be easily controlled, and a porous body made of a dried gel can be obtained more easily.
[0034]
The binder used in the present invention is preferably used in a state dispersed or dissolved in a solvent. As the solvent, water and organic solvents (including mixed solvents) are used, and there is no particular limitation as long as it dissolves and disperses the binder. For example, the binder using water as a solvent includes starch, cellulose, melamine, phenol resin, isocyanate, resorcin, vinyl acetate resin emulsion, and acrylic resin emulsion. Examples of the binder using an organic solvent as a solvent include silicon resin (silicone resin), acrylic resin, vinyl resin, vinyl acetate resin, phenol resin, and cellulose. Among these, what forms a crosslinked structure by heating, light irradiation, and catalytic action at the time of dry molding is preferable because a stronger one can be obtained.
[0035]
The manufacturing method of the molded object containing the dry gel of embodiment by this invention includes the following processes.
[0036]
The volume of the pores having a pore diameter in the range of 2 nm to 40 nm as described above is 1 cm. ^Three A dry gel powder that is less than or equal to / g is prepared, and a binder composition containing a binder and a solvent is prepared. The dry gel powder is molded into a predetermined shape using this binder composition.
[0037]
After mixing the dried gel powder and the binder composition, the composition is formed into a predetermined shape. For example, a block-shaped or film-shaped molded body can be obtained by pouring a composition containing a dry gel powder into a mold, coating, or printing. Alternatively, after the dry gel powder is filled into a mold having a predetermined shape, the binder composition may be filled (injected) into the mold.
[0038]
Thereafter, by drying the solvent contained in the composition, a binder enters the pores of the dried gel powder, and a molded body in which the dried gel particles are bonded is obtained. At this time, before the solvent is dried or when the solvent is dried, the binder is polymerized by light irradiation, heat, or addition of a catalyst to obtain a stronger molded body. The binder is preferably about 30% or less of the mass of the dried gel powder so as not to excessively increase the density of the molded body.
[0039]
Since the molded body containing the dried gel thus obtained has a low density, it has high heat insulation when used as a heat insulating material, and low in air and various gases when used in an acoustic matching layer of an ultrasonic transducer. Matching to acoustic impedance is easy. Furthermore, since the strength is higher than the conventional one, the handleability is excellent, and there is an effect that the application to the above-mentioned use is easy. In addition, since shrinkage and cracking due to contact with water and organic solvents are suppressed, restrictions on the usage environment are greatly eased when applied to heat insulating materials, acoustic matching layers, sound absorbing materials, catalyst carriers, insulating materials, etc. There is an effect.
[0040]
Moreover, the composition obtained by mixing the above-mentioned dry gel powder, binder, and solvent typically has a dry gel dispersed in a slurry form. The binder component (solid content) in the composition is preferably adjusted to about 30% by mass or less with respect to the mass of the dried gel so that the density of the molded body after drying does not increase excessively. Also, since the binder and solvent penetrate into the pores of the dry gel, the dry gel powder can be easily removed from the composition as in the case of dispersing the conventional hydrophobized dry gel particles in the aqueous emulsion binder composition. Thus, a stable composition can be obtained without floating or separating, and the workability of the molding process is also improved.
[0041]
(Dry gel powder)
First, the dry gel powder used suitably for the molded object containing the dry gel by this invention and its manufacturing method are demonstrated in detail.
[0042]
Below, the effect of the present invention is remarkable, and the density is 500 kg / m. ^Three The method for producing the following dry gel is exemplified, but using the production method of the present invention, 500 kg / m ^Three It is also possible to produce dried gels of super density.
[0043]
The step of producing a dry gel in the method for producing a molded article including a dry gel according to an embodiment of the present invention includes a step of preparing a first gel having a first solid skeleton and a first pore, A restructuring step (also referred to as a second gelation step) that decomposes at least a part and forms a second solid skeleton thicker than the first solid skeleton. The 1st gel can use what was manufactured by the well-known method.
[0044]
The restructuring step is executed by a step of bringing the first gel into contact with a restructuring raw material solution (also referred to as a “second gel raw material solution”) that generates particles having a particle size of 10 nm to 100 nm.
[0045]
The step of preparing the first gel can be performed by a known method, for example, a sol-gel from a first gel raw material solution containing a first gel raw material, a first catalyst (gelation catalyst), and a first solvent. Producing a first wet gel by the method. This process may be referred to as a first gelation process. Here, the density after drying is 500 kg / m. ^Three The following wet gel is prepared.
[0046]
In the restructuring step, the restructuring raw material solution (second gel raw material solution) in contact with the first gel is, for example, a restructuring raw material (second gel raw material), a restructuring catalyst (second catalyst), water, And a restructuring solvent (second solvent). The restructuring raw material may be the same as the first gel raw material, and the restructuring catalyst may be the same as the first catalyst. The restructuring raw material solution needs to contain water, and it is preferable to use a solution in which particles having a particle size of 10 nm to 100 nm are generated in the restructuring raw material solution.
[0047]
It is preferable that the 1st gel contacted with a reconstruction raw material solution is a wet gel (1st wet gel). As illustrated here, the density after drying is 500 kg / m. ^Three When the wet gel is dried, the gel may crack in the process. However, when the wet gel is left in contact with the reconstituted raw material solution, the density of the first gel is low even if it is a low-density gel. Occurrence of cracks due to rising or collapse of the solid skeleton is prevented. When the final dry gel is used in the form of powder (including granules), the wet gel may be dried and then subjected to a reconstruction process. In this case, it is preferable to hydrophobize the surface of the solid skeleton of the first gel. This hydrophobizing step can be performed by a known method.
[0048]
This reconstruction process is not limited to one time, and may be executed a plurality of times stepwise. In addition, the second wet gel formed by the restructuring step is brought into contact with an aqueous solution containing the third catalyst to further decompose a part of the second solid skeleton, and further to a gel reinforcing step for increasing the strength of the second solid skeleton. You may have.
[0049]
Moreover, the process of hydrophobizing the surface of the obtained 2nd solid frame | skeleton may further be included, and a hydrophobization process may be performed after a reconstruction process, and it performs by the same process as a reconstruction process. Also good. Of course, the hydrophobizing step may be performed after the second wet gel having the second solid skeleton obtained by the restructuring step is dried.
[0050]
An outline of the mechanism by which a dry gel that hardly undergoes shrinkage and / or cracking due to contact with an organic solvent or the like by the method for producing a dry gel in the embodiment of the present invention will be described.
[0051]
First, in the first gelation step, the solid skeleton of a wet gel having a relatively low density (for example, the density after drying is 500 kg / m 2). ^Three In the restructuring step (second gelation step), a monomer or oligomer that becomes the restructuring raw material (second gel raw material) is polymerized on the first solid skeleton formed in the first gelation step. The fine particles thus formed are mainly polymerized to reinforce the thin portions of the first solid skeleton and form a second solid skeleton that is thicker than the first solid skeleton, while the density increases. In this way, after forming the solid skeleton of the gel once, it has a gelation step again, so it is possible to improve the density in the state of a wet gel, and it is also possible to obtain a high-density dry gel that was not obtained conventionally Become.
[0052]
In the reconstruction process, the decomposition (dissolution) of the first solid skeleton also proceeds in parallel with the increase in density due to the above-described polymerization. That is, hydrolysis of the first solid skeleton occurs in parallel due to the presence of water in the restructuring raw material solution and the restructuring catalyst (second catalyst). Therefore, the fine pore structure of the first gel disappears, and the reconstruction of the gel structure having the second solid skeleton thicker than the first solid skeleton and the coarse pores is promoted.
[0053]
In addition, according to the manufacturing method of the embodiment of the present invention, the shrinkage of the wet gel that progresses during gelation is suppressed, and therefore, when a dry gel is formed on a substrate or the like, cracks and dropping off from the substrate are reduced. Effect is obtained. This can be explained as follows.
[0054]
In general, during gelation, as the cross-linking progresses, the gel with a higher initial density causes a reduction in size due to shrinkage. However, since the manufacturing method of the dry gel of embodiment of this invention has a 1st gelation and a reconstruction process, the gel density in the 1st gelation process required in order to obtain a gel of a fixed density is obtained. As a result, shrinkage in the first gelation step can be suppressed.
[0055]
The gel strength can also be improved by the conventional aging treatment in which the first wet gel is left in the solution at a constant temperature without adding the gel raw material to the first gel raw material solution for producing the first wet gel. Are known. In this conventional aging treatment, it is considered that the gel strength increases because dehydration condensation proceeds between the hydroxyl groups in the narrow portion of the first solid skeleton to strengthen the bond. However, in this case, since the gel raw material is not replenished, the effect of thickening the skeleton is small, and a sufficient strength improvement cannot be obtained.
[0056]
In the method described in Patent Document 1 described above, since the gel raw material is reinforced, the above-described aging treatment is improved in strength, but most of small pores of 2 to 40 nm remain, so that organic It is not possible to obtain sufficient strength to avoid contact with a solvent, cracking due to drying, and cracking.
[0057]
In any method, since the solid skeleton (first solid skeleton) of the gel formed first is not decomposed, fine pores remain as they are, and the capillary force generated in the pores is reduced. It is thought that it is not done.
[0058]
In the following, embodiments relating to the production method of the present invention will be described in more detail.
[0059]
As shown in FIG. 1, the method for producing a porous body made of a dried gel according to the present embodiment is a step S <b> 1 of preparing a first gel raw material solution (including a first gel raw material, a first catalyst, and a first solvent) 1. And a step S2 for producing the first wet gel 2 from the first gel raw material solution 1, and a reconstructed raw material solution prepared separately from the first wet gel 2 (including a restructuring raw material, a restructuring catalyst, water and a restructuring solvent) .) 3 is brought into contact with S3, and in the reconstituted raw material solution 3, a second wet gel 4 having a second solid skeleton thicker than the solid skeleton of the first wet gel 2 is prepared. . Further, a hydrophobization step is performed after step S4, and the hydrophobized second wet gel is dried, thereby obtaining a dry gel that hardly causes shrinkage and / or cracking due to contact with an organic solvent or the like. As will be described later, the dry gel thus obtained has a pore volume of 1 cm in a pore diameter range of 2 nm to 40 nm. ^Three / G or less.
[0060]
In the present specification, unless otherwise specified, “pore volume” is the pore volume calculated using the BJH method by the nitrogen adsorption method, and “specific surface area” is the BET method using the nitrogen adsorption method. The specific surface area calculated as above.
[0061]
Each step will be described in turn below.
[0062]
(First gelation step)
In the present embodiment, first, the first wet gel 1 is prepared by a so-called sol-gel method (S1 to S2 in FIG. 1). In that case, a 1st catalyst (gelation catalyst) is added to a 1st gel raw material, and gelatinization is advanced.
[0063]
As the gel material used in the manufacturing method of the present embodiment, a general material used in the sol-gel method is used. For example, there are oxide fine particles such as silicon, aluminum, zirconium and titanium, and corresponding alkoxides. Among these, a compound containing silicon as a metal is preferable from the viewpoint of availability. In the case of the metal alkoxide, as already described, silicon is preferable from the viewpoint of easy reaction control. For example, tetraalkoxysilanes such as tetramethoxysilane and tetraethoxysilane, and silicon alkoxides such as trialkoxysilane and dialkoxysilane are used.
[0064]
Here, since dialkoxysilane is difficult to form a gel by itself, it is used by mixing with other gel raw materials. Furthermore, when these oligomers are used as the gel raw material, the boiling point of the gel raw material is lowered, so that the safety at the time of production is enhanced. In addition, colloidal silica, water glass, and an aqueous silicic acid solution obtained by electrodialysis from water glass are preferably used because of their low price.
[0065]
As the gelation catalyst, a general organic acid, inorganic acid, organic base, or inorganic base is used. Examples of organic acids include acetic acid and citric acid, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, organic bases such as piperidine, and inorganic bases such as ammonia. In addition, use of an imine type such as piperidine is more preferable from the viewpoint of reducing capillary force because of the effect of increasing the pore diameter.
[0066]
Examples of the first solvent include lower alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol and diethylene glycol, mono- or diethers of ethylene glycol and diethylene glycol, lower ketones such as acetone, lower ethers such as tetrahydrofuran and 1,3-dioxolane. Such water-soluble organic solvents are used. In addition, when a gel is formed by hydrolysis or condensation polymerization of the first gel raw material, water necessary for hydrolysis is also added.
[0067]
(Reconstruction process)
Subsequent to the first gelation step, a reconstruction step (S3 to S4 in FIG. 1) is performed. In the restructuring step, a new solid skeleton (second solid skeleton 4) is formed while decomposing some part of the solid skeleton of the first wet gel 2 formed in the first gelation step. Specifically, first, a reconstituted raw material solution 3 is prepared by adding and mixing a reconstructed raw material for the restructuring step, a reconstructed catalyst and water, and a solvent as necessary (S3). The 1st wet gel 1 obtained by 1 gelation process is immersed.
[0068]
Addition of the restructuring catalyst promotes polymerization and accelerates the growth of a new solid skeleton. Moreover, the addition of water and a restructuring catalyst acts to break down the fine pore structure of the first wet gel by advancing decomposition (dissolution) of the fine particles constituting the solid skeleton of the first wet gel by hydrolysis. Furthermore, this hydrolysis is also accelerated by the restructuring catalyst described above. As described above, since the speed of breaking the old solid skeleton (first solid skeleton) and the speed of forming the new solid skeleton (second solid skeleton) are both very high, the solid with a significant change in pore structure. It is thought that skeleton reconstruction will be possible for the first time.
[0069]
This will be described with reference to FIGS. 2 (a) and 2 (b). FIG. 2 (a) is a diagram schematically showing the first solid structure 2a of the first wet gel 1, and FIG. 2 (b) shows the second solid skeleton 4a of the second wet gel 4 obtained by this embodiment. This is shown schematically. These FIG. 2 is based on the SEM observation result of the dry gel obtained by the Example mentioned later.
[0070]
The first solid skeleton 2a shown in FIG. 2 (a) is composed of particles of several nm, and the volume of pores of 2 nm to 40 nm is 3 cm. ^Three / G-5cm ^Three / G or so. In the conventional method for producing a dry gel, the wet gel is hydrophobized and then dried. However, since there are many fine pores, the gel contracts or cracks as described above. That is, it was difficult to obtain a dry gel having the structure shown in FIG.
[0071]
In contrast, in the second solid skeleton 4a of the second wet gel 4 according to the present embodiment, a part of the first solid skeleton 2a is decomposed and fine particles generated by gelation of the reconstructed raw material are included. By bonding, a second solid skeleton 4a mainly composed of particles of about 10 nm to about 100 nm is formed. At this time, the volume of pores of 2 nm to 40 nm is 1 cm. ^Three / G or less. Therefore, even if the 2nd wet gel 4 is dried after a reconstruction process, generation | occurrence | production of the shrinkage | contraction of a gel and a crack are suppressed. In addition, in this way, the fine pores that cause shrinkage during infiltration and drying of the organic solvent are greatly reduced, so that shrinkage and cracking when in contact with the organic solvent can be suppressed. .
[0072]
This phenomenon will be described with specific experimental results.
[0073]
FIGS. 3A to 3E are graphs showing the results of measuring the particle size distribution of particles generated in the reconstructed raw material solution (the same composition as in Example 1 described later). The particle size distribution was measured by measuring Doppler shift due to Brownian motion of particles using dynamic scattering. This measurement was performed using a particle size distribution meter (MICROTRAC UPA150) manufactured by Nikkiso Co., Ltd. FIG. 3 (a) shows the results 1 hour after preparation of the solution, (b) 5 hours, (c) 10 hours, (d) 24 hours, and (e) 48 hours. In addition, since the amount of particles produced was small and the scattering intensity was weak until 1 hour after the solution was prepared, highly reliable data could not be obtained.
[0074]
3A to 3E show that particles of about 30 nm to 100 nm are formed over several hours to 10 hours in this reconstructed raw material solution. Note that relatively large particles are formed in the initial hours, and many relatively small particles are formed over time. This is thought to be due to an inhomogeneous reaction in the initial stage. Moreover, there is a possibility that the large particles once formed are decomposed over time.
[0075]
When the first wet gel is immersed in such a solution, among the 30 nm to 100 nm particles present in the reconstituted raw material solution, relatively small particles with high reactivity (large specific surface area) are preferentially selected. Polycondensates to a solid skeleton of gel. In parallel with this, the monomer or oligomer is dissolved (hydrolyzed) from the first solid skeleton, so that the reconfiguration of the solid skeleton proceeds.
[0076]
According to the results of various studies, the diameter of the particles contributing to the condensation polymerization depends on the particle size distribution of the treatment liquid, and when the same number of 10 nm to 50 nm particles are distributed, the reconstituted gel is reactive. In the case where almost the same number of particles of 40 nm to 100 nm are distributed, the relatively small particles of about 40 nm to 60 nm are considered to mainly contribute to the condensation polymerization. . Therefore, in order to perform efficient reconstruction, it is considered preferable to use a gel raw material solution that generates particles having a particle size of 10 nm to 100 nm as the restructuring raw material solution.
[0077]
In addition, when the particles are usually large, the reactivity such as polymerization is reduced and the bonding between the particles is weakened. However, according to the production method of the present embodiment, particles of 10 nm to 100 nm are formed in the reconstituted gelling solution. And immediately polymerizes onto the first solid skeleton (bonds to the surface of the first solid skeleton). That is, since the surface of the generated particles reacts with the first solid skeleton in a state of rich reactivity (activity), the reaction proceeds quickly. Furthermore, since the neck portion between the particles constituting the first solid skeleton is highly active and has a high degree of freedom of deformation, this neck portion is particularly likely to be thick, and there is an effect that the bonding between the particles can be strengthened.
[0078]
Next, with reference to FIGS. 4A and 4B, it will be described that a second wet gel having a large pore diameter is formed by the reconstruction process. FIG. 4 (a) shows the cumulative pore curve (pore volume (cm) determined by the BJH method using nitrogen gas. ^Three / G) and a pore diameter (pore diameter)), and FIG. 4B is a graph showing a differential pore curve. In each figure, the curves C and D show the cumulative and differential pore curves of the first wet gel (after drying), and the curves A, B and E show after the reconstruction process according to the present embodiment, that is, The cumulative and differential pore curves of 2 wet gels (after drying) are shown. A curve F represents a cumulative pore curve of a wet gel (after drying) in which the skeleton of the first wet gel is reinforced by the method described in Patent Document 1 described above.
[0079]
As is clear from FIGS. 4 (a) and (b), the first wet gel (curves C and D) has a pore volume of 3 cm to 2 nm or more and 40 nm or less. ^Three / Cm or more, by passing through the reconstruction process of this embodiment, 1 cm ^Three / G or less (curves A, B and E). Especially for the sample of curve E, 0.4 cm ^Three / G or less.
[0080]
Thus, it is thought that a part of 1st solid skeleton has collapse | crumbled by hydrolysis because the volume of a pore with a small pore diameter reduces by a reconstruction process.
[0081]
On the other hand, in the method of Patent Document 1, the pore volume of pores having a pore diameter of 2 nm to 40 nm is 2 cm. ^Three / G, and no collapse or reconstruction of the first solid framework has occurred.
[0082]
Furthermore, the pore volume is reduced to 0.5 cm by increasing the treatment time of the reconstruction process or increasing the concentration of the catalyst and / or water. ^Three / G or less. At this time, the specific surface area is also 300 m. ² / G or less.
[0083]
This is the structure of the porous body which consists of a preferable dry gel of this invention. In this case, not only shrinkage does not occur due to contact with the organic solvent, but also occurrence of cracks can be avoided. Further, when the reconstituted wet gel is dried, there is an effect that a porous body made of a block-shaped dry gel without cracking and shrinkage can be obtained by ordinary heat drying, without depending on supercritical drying.
[0084]
In addition, the dry gel obtained in this embodiment has a remaining amount of functional groups (functional groups that have not been consumed for gelation) of about several tens of percent less than conventional dry gels. For example, as shown in Table 1, when the first gel is formed using alkoxysilane, the functional group (alkoxy group) in which the dried gel according to the present invention that has undergone the restructuring process remains as compared with the conventional dried gel. And the ratio of silanol groups) is halved. The dry gels exemplified in Table 1 are all hydrophobized with dimethyldimethoxysilane, and the number of Si atoms having a functional group is ²⁹ It determined by Si-NMR measurement.
[0085]
[Table 1]

[0086]
In general, a gel formed using alkoxysilane has a small number of particles forming a solid skeleton and a large number of functional groups on the particle surface that do not contribute to polymerization. According to the manufacturing method of the present embodiment, the surface area is reduced because the particles of 10 to 100 nm formed in the restructured gel raw material solution mainly form a new skeleton, that is, bind to the surface of the solid skeleton of the first gel. Accordingly, it is considered that the functional groups left on the surface are also reduced accordingly. When the dried gel according to the present embodiment is observed with an SEM, the presence of particles of about 10 nm to several tens of nm can be confirmed on the surface of the solid skeleton.
[0087]
In addition, the reconstitution catalyst and water addition concentrations allow the restructuring to proceed sufficiently even at room temperature or lower. preferable.
[0088]
In the restructuring step, it is important to selectively proceed on the solid skeleton of the wet gel, not the outside of the wet gel formed by the first gelation. For that purpose, it is preferable to lengthen the time required for gelation in order for the reconstituted gel raw material to sufficiently enter the first wet gel. Alternatively, it is preferable that the wet gel is made into small pieces or particles or a thin film so that the reconstructed gel raw material enters the wet gel in a short time.
[0089]
As already mentioned, by forming a low-density gel skeleton in the initial stage, the shrinkage during gelation is reduced, so cracking due to shrinkage and missing from the substrate are reduced, and heat insulation, sound absorbing material, insulating material, acoustic matching When used as a layer or the like, good performance is ensured and variations in characteristics are reduced. In addition, since the pore diameter of the porous body is increased, cracks and shrinkage that occur in the drying process when contacted with an organic solvent due to an accident or the like are reduced, and the reliability during use is enhanced.
[0090]
As the reconstruction catalyst used in the reconstruction process, those in the group of gelation catalysts used in the first gelation process can be used, and in particular, the same as the gelation catalyst in the first gelation process. Need not be.
[0091]
Further, as the reconstructed gel raw material used in the restructuring step, the gel raw material used in the first gelation step is used, and the relationship between the first gel raw material and the reconstructed gel raw material is not particularly limited. For example, when tetraethoxysilane, which is an alkoxysilane, is used as the gel material in the first gelation step, tetraethoxysilane can be used as the reconstructed gel material in the reconstruction step, If a solvent to be dissolved is selected, other metal alkoxides and aqueous silicic acid solutions can also be used.
[0092]
The solvent used in this step is not particularly limited as long as the reconstructed gel raw material and the reconstructed catalyst are dissolved as described above.
[0093]
(Hydrophobicization process)
Following the reconstruction process, a hydrophobization process is performed. In this step, a hydrophobic group is introduced by reacting a hydrophobizing agent dissolved in a solvent with the surface of the wet gel obtained up to the restructuring step. In the case of chlorosilane or the like, which will be described later, the hydrophobizing agent reacts with water and decreases its reactivity with the wet gel surface. It is preferable to remove water by distilling off using a boiling solvent.
[0094]
The hydrophobizing agent used in the present invention is preferably a silylating agent from the viewpoint of high reactivity, and examples thereof include silazane compounds, chlorosilane compounds, alkylsilanol compounds and alkylalkoxysilane compounds.
[0095]
In the case of a silazane compound, a chlorosilane compound, or an alkylalkoxysilane compound, these silylating agents react with silanol groups on the gel surface after being directly or hydrolyzed to the corresponding alkylsilanol. Further, when alkylsilanol is used as a silylating agent, it reacts with the silanol group on the surface as it is.
[0096]
Among these, chlorosilane compounds and silazane compounds are particularly preferred because of their high reactivity during hydrophobization and availability, and because they are easily available and do not generate gases such as hydrogen chloride and ammonia during hydrophobization. Alkyl alkoxysilanes are particularly preferably used.
[0097]
Specifically, chlorosilane compounds such as trimethylchlorosilane, methyltrichlorosilane and dimethyldichlorosilane, silazane compounds such as hexamethyldisilazane, methoxytrimethylsilane, ethoxytrimethylsilane, dimethoxydimethylsilane, dimethoxydiethylsilane and diethoxydimethylsilane There are silylating agents represented by silanol compounds such as alkylalkoxysilane compounds, trimethylsilanol and triethylsilanol. If these are used, hydrophobization can be promoted by introducing an alkylsilyl group such as a trimethylsilyl group into the wet gel surface.
[0098]
Further, if a fluorinated silylating agent is used as the hydrophobizing agent, the hydrophobicity becomes strong and is very effective.
[0099]
As the hydrophobizing agent, alcohols such as ethanol, propanol, butanol, hexanol, heptanol, octanol, ethylene glycol and glycerol as well as carboxylic acids such as formic acid, acetic acid, propionic acid and succinic acid can be used. . These are hydrophobized by reacting with the hydroxyl groups on the gel surface to form ethers or esters, but the reaction is relatively slow and requires high temperature conditions.
[0100]
(Drying process)
Following the hydrophobization step, a drying step is performed. In this step, a dry gel is obtained by removing the solvent from the wet gel obtained up to the hydrophobization step.
[0101]
There are three drying methods for removing the solvent from the wet gel: (1) heat drying method (2) supercritical drying method (3) freeze drying method. The heat drying method is the most common and simple drying method, and the wet gel containing the solvent is heated to vaporize and remove the solvent in the liquid state. This drying is most preferable. In addition, "heat drying" here includes natural drying in which the above-described degree of heating is extremely low and left to dry without heating.
[0102]
When drying, if the gel density is low, the gel may temporarily shrink and crack due to capillary forces proportional to the surface tension of the solvent in the gel. For this reason, the solvent for drying is preferably a hydrocarbon-based solvent having a low surface tension at the boiling point, and particularly inexpensive hexane, pentane or a mixture thereof is preferable. On the other hand, from the viewpoint of safety, drying from alcohols such as isopropanol, ethanol, butanol, and water or a mixed solvent of water and an organic solvent is preferable. In this embodiment, the wet gel has a pore volume of 0.5 cm by the supercritical drying method described later. ^Three / G or less, specific surface area of 300m ² If it is a wet gel that gives a dry gel of / g or less, cracking and shrinkage are suppressed even by drying from many solvents such as alcohols and water.
[0103]
The supercritical drying method uses a supercritical fluid having a surface tension of 0 in order to lower the surface tension of the solvent when the solvent is removed. Upon drying, the solvent is removed without going through a liquid state. As the supercritical fluid used for drying, there are supercritical states such as water, alcohol, carbon dioxide, etc., but carbon dioxide that can be obtained at the lowest temperature and is harmless is preferably used.
[0104]
Specifically, by first introducing liquefied carbon dioxide into the pressure vessel, the solvent in the wet gel in the pressure vessel is replaced with liquefied carbon dioxide. Next, the pressure and temperature are raised to a critical point or higher to achieve a supercritical state, and carbon dioxide is gradually released while maintaining the temperature to complete drying.
[0105]
The lyophilization method is a drying method in which after the solvent in the wet gel is frozen, the solvent is removed by sublimation. Since it does not go through a liquid state, a gas-liquid interface does not occur in the gel, and capillary force does not work, so that shrinkage of the gel during drying can be suppressed.
[0106]
The solvent used in the freeze-drying method is preferably a solvent having a high vapor pressure at the freezing point, and examples thereof include tertiary butanol, glycerin, cyclohexane, cyclohexanol, para-xylene, benzene, and phenol. Among these, tertiary butanol and cyclohexane are particularly preferable because of high vapor pressure at the melting point.
[0107]
At the time of lyophilization, it is effective to replace the solvent in the wet gel with a solvent having a high vapor pressure at the above-mentioned freezing point. In addition, it is more preferable to use a solvent having a high vapor pressure at the freezing point as the solvent used for the gelation because the solvent replacement can be omitted and efficient production becomes possible.
[0108]
Drying may be performed after the hydrophobizing step or may be performed before the hydrophobizing step. In the case of hydrophobizing after the drying step, hydrophobic groups are introduced on the surface of the dried gel by exposing the dried gel to the vapor of the hydrophobizing agent, not in the solution. Therefore, there is an effect that the amount of solvent to be used is reduced.
[0109]
As the hydrophobizing agent used at this time, the above-mentioned hydrophobizing agents can be used, but chlorosilane compounds such as trimethylchlorosilane and dimethyldichlorosilane are most preferable because of their high reactivity. When using a hydrophobizing agent other than the chlorosilane compound, it is also effective to use a catalyst that can be introduced in a gaseous state, such as ammonia or hydrogen chloride.
[0110]
Further, when hydrophobizing in the gas phase, the temperature during hydrophobizing can be increased without being limited by the boiling point of the solvent or hydrophobizing agent. Therefore, hydrophobization in the gas phase is effective for speeding up the reaction. Moreover, if the wet gel is a thin film or powder, the penetration of the hydrophobizing agent vapor is easy, and the thin film is more preferable because the effect of reducing the amount of solvent is great.
[0111]
Moreover, it is also possible to perform a reconstruction process and a hydrophobization process simultaneously. In this case, since the two steps are simultaneously performed, an effect that a porous body made of a dry gel can be obtained in a short time is obtained.
[0112]
Specifically, in the restructuring step and the hydrophobizing step, the wet gel obtained in the first gelation step is immersed in a treatment liquid in which the restructuring gel raw material solution used in the restructuring step and the hydrophobizing agent are mixed. It will be implemented. By doing so, gel reconstruction and hydrophobization proceed simultaneously. As the restructuring raw material and the hydrophobizing agent at the time of hydrophobization, the same ones as described above can be used. For example, after the first gelation is performed from an aqueous silicic acid solution obtained by electrodialysis from water glass, the obtained wet gel is converted into a gel raw material alkoxysilane and a hydrophobizing agent by using a water-soluble solvent. In a solution in which a silazane compound or the like is dissolved, restructuring and hydrophobization are performed simultaneously.
[0113]
When the restructuring step and the hydrophobizing step are simultaneously performed as described above, the combination of the gel raw material and the hydrophobizing agent is not particularly limited as long as solubility is satisfied. In addition, when a polyfunctional alkylalkoxysilane, chlorosilane, or alkylsilanol having an alkyl group is used as the hydrophobizing agent, the alkyl group is introduced into the gel skeleton, which gives the gel flexibility and brittleness. There is also an effect that is improved. At this time, the central part of the gel skeleton is hard and the peripheral part has a characteristic structure with flexibility.
[0114]
As described above, a dry gel having a hydrophobic surface of the solid skeleton can be obtained. Moreover, in the above-described manufacturing process, a dry gel having a hydrophilic surface of the solid skeleton can be obtained by omitting the hydrophobic step. The wet gel that has undergone the restructuring process has reduced fine pores and a thick solid skeleton, so that even if the surface remains hydrophilic and drying treatment (including heat drying) is performed, the gel shrinkage and Generation of cracks is suppressed. For example, when a solid skeleton is formed with a metal oxide, a dry gel having a hydrophilic surface on the surface of the solid skeleton can be obtained.
[0115]
(Crushing process)
A dried gel powder is obtained by pulverizing the dried gel obtained as described above by a known method. The pulverization is performed using, for example, a blender (for example, 700S type manufactured by Walling). The particle size of the dry gel powder is not particularly limited, and may be a powder of the order of several tens of micrometers. From the viewpoint of ease of pulverization, it is preferable to use a dry powder in the range of 1 μm to 100 μm. In addition, a wider particle size distribution is preferable because the filling property is improved.
[0116]
Moreover, you may perform a grinding | pulverization process between a 1st gelatinization process and a drying process. In addition, for example, the first wet gel may be pulverized in the solution by stirring or the like while the first wet gel is produced or after the first wet gel is produced. Thus, if it grind | pulverizes in the stage of a 1st wet gel, the advantage that the process efficiency in a subsequent reconstruction process and / or a drying process will improve is acquired. Moreover, the wet gel on particle | grains can also be obtained by performing a 1st gelation process in the state which disperse | distributed the 1st gel raw material solution in the poor solvent.
[0117]
(Binder composition)
The binder composition (binder and solvent) is selected according to the solvent affinity (hydrophilic or hydrophobic) of the dry gel powder and / or depending on the application of the molded body. Since the dried gel is excellent in solvent resistance, various binder compositions can be used.
[0118]
A method of mixing the binder composition and the dry gel powder to obtain a molding composition can be performed by a known method. For example, it can mix using a mortar, a ball mill, a homogenizer, etc.
[0119]
Moreover, you may mix a reinforcing material in the composition for shaping | molding. Alternatively, the molding composition can be poured into a reinforcing material to form a molded body containing the reinforcing material. As the reinforcing material suitably used, honeycomb structure, glass fiber or mineral fiber, organic fiber (for example, natural fiber in addition to synthetic fiber such as polyester fiber, aramid fiber, nylon fiber, etc.) or these fibers Fiber aggregates such as fiber cloths and nonwoven fabrics made of fibers can also be used. Polyurethane, polyester, vinyl chloride, polyolefin, polystyrene, silicone, and other foams can also be used.
[0120]
Moreover, you may form a protective film on the surface of a molded object. By forming the protective film, there is an effect that the strength of the surface increases and the handling becomes easier.
[0121]
(Molded body containing hydrophobic dry gel powder)
An embodiment in which a molded body is produced using a hydrophobic dry gel powder and a hydrophobic binder composition will be described. The hydrophobic dry gel powder as used herein means a dry gel powder that floats in water when the dry gel powder is mixed with water, and water does not substantially penetrate into the pores. To do. Such hydrophobicity is imparted by performing the above-described hydrophobizing step, and hydrophobicity can be easily imparted if it is an inorganic oxide-based dry gel. Moreover, even if it is an organic type gel, if it reacts with the hydrophobizing agent mentioned above, hydrophobicity can be provided.
[0122]
When the dry gel powder has hydrophobicity, in the conventional molding method, the gel shrinks when the organic solvent in the molding composition penetrates into the pores of the gel and is dried. The density increases. On the other hand, in this embodiment, the pore volume corresponding to pores of 2 nm or more and 40 nm or less is 1.0 cm. ^Three By using a dry gel powder as small as / g or less, the capillary force proportional to the pore diameter is reduced, and the gel shrinkage is suppressed.
[0123]
Any binder that can be dissolved in an organic solvent can be used. As described above, general binders such as silicon resin, acrylic resin, vinyl resin, vinyl acetate resin, phenol resin, and cellulose can be used.
[0124]
In addition, when a conventional hydrophobic dry gel is used, water does not enter into the pores because the gel is hydrophobic, but a mixed solvent of an organic solvent and water enters into the pores of the gel. Sometimes. Capillary force generated when a water-containing solvent forms a gas-liquid interface in the pores is large, and shrinkage is significant in a molded body made of a conventional dry gel, but the dry gel of the embodiment of the present invention is used. In such a case, shrinkage of the molded body is suppressed.
[0125]
(Molded product containing hydrophilic dry gel powder)
An embodiment in which a molded body is produced using a dry gel powder having hydrophilicity and a hydrophilic binder composition will be described. The dry gel powder having hydrophilicity as used herein refers to a dry gel powder that absorbs water when the dry gel powder is poured into water.
[0126]
When the dried gel powder has hydrophilicity, in the conventional molding method, water or an organic solvent in the molding composition penetrates into the pores of the gel, and this penetration and drying Gel shrinkage occurs and the density of the molded body increases. In the present embodiment, the pore volume corresponding to pores of 2 nm or more and 40 nm or less is 1.0 cm. ^Three By using a dry gel powder as small as / g or less, even when water is contained in the solvent, the capillary force proportional to the pore diameter is reduced and the gel shrinkage is suppressed.
[0127]
Further, in the conventional method for producing a molded article comprising a dry gel, in order to obtain a low-density molded article, it is necessary to prevent the penetration of a solvent into the gel. There was no choice but to combine a binder with an aqueous solvent. When the dried gel has hydrophobicity, the gel surface is covered with hydrophobic organic groups such as alkyl groups that form a low-energy surface. The interaction is weak, and the binding force (adhesive force) by the binder is reduced.
[0128]
On the other hand, when the dry gel powder has hydrophilicity as in the present embodiment, an attractive interaction works strongly with the polar group of the binder, so that the binding force by the binder is enhanced. . Furthermore, when the polar group on the surface of the solid skeleton of the dry gel reacts with the polar group of the binder to form a bond, a molded body with higher strength can be obtained. For example, when a hydroxyl group is present on the surface of the dry gel powder and shows hydrophilicity, for example, by reacting with an isocyanate group, a hydroxyl group, an epoxy group, a carboxyl group, a methoxymethyl group, etc. of the binder, a urethane bond, An ether bond, an ester bond, and a methylene bond are formed.
[0129]
As the binder used in the present embodiment, those described above can be used, and a binder having a polar group such as a hydroxyl group is particularly preferable.
[0130]
As the dry gel powder used in the present embodiment, the above-mentioned dry gel powder can be used regardless of whether it is organic or inorganic as long as it has hydrophilicity. In particular, a metal oxide-based dry gel powder made of silicon oxide or the like can be suitably used because it has a large number of hydroxyl groups on the surface. In the case of the above metal oxide-based dry gel, the binder has a silanol group or a silanol group by hydrolysis or the like in addition to those having an isocyanate group, a hydroxyl group, an epoxy group, a carboxyl group, and a methoxymethyl group as described above. Use of the resulting silanol-based or alkoxysilane-based binder is preferable because it is easy to form a bond by condensation of silanol groups.
[0131]
In addition, as described above, after forming a dry gel powder having hydrophilicity, the remaining hydroxyl groups are reacted with a hydrophobizing agent in the gas phase to impart hydrophobicity. Is also possible.
[0132]
Hereinafter, the present invention will be described based on specific examples. However, the present invention is not necessarily limited to the contents of the specific gel raw materials, the types of raw materials such as the gelation catalyst, the solvent, and the binder used below. It is not something.
[0133]
【Example】
<< Example 1 and Comparative Example 1 >>
In this example, a molding composition was prepared by mixing a hydrophobized dry gel powder, an organic solvent, and a binder, and a molded body was prepared using the composition.
[0134]
(1) First gelation step
First, tetraethoxysilane / ethanol / water / hydrogen chloride = 1/15/1 / 0.00078 (molar ratio) was mixed and placed in a thermostatic bath at 65 ° C. for 3 hours to hydrolyze tetraethoxysilane. Made progress. Next, water / NH _Three = 2.5 / 0.0057 (molar ratio with respect to tetraethoxysilane) was added and mixed, and placed in a thermostatic bath at 50 ° C. for 1 day to proceed with gelation to obtain a wet gel. At this point, the wet gel was cut into a shape of 10 mm × 10 mm × 3 mm.
[0135]
(2) Restructuring process
Tetraethoxysilane was used as a restructuring raw material (second gel raw material), and ammonia water was used as a restructuring catalyst (second catalyst). The wet gel obtained in the first step of gelation is immersed in a restructured raw material solution (second gel raw material solution) obtained by mixing with tetraethoxysilane / ethanol / ammonia water = 60/35/5 (volume ratio). It piled up and processed in a 70 degreeC thermostat. The treatment time was three cases of 9 hours, 10.5 hours, 13 hours, and 24 hours separately. Ammonia water was 0.1N, and the second gel raw material solution was 20 times the wet gel volume.
[0136]
(3) Hydrophobization process
The wet gel obtained in the restructuring step was washed twice by immersing it in isopropyl alcohol having a volume 5 times the gel volume. The wet gel was hydrophobized while being mixed with a hydrophobizing solution obtained by mixing dimethyldimethoxysilane / isopropyl alcohol / ammonia water = 45/45/10 (weight ratio) at 40 ° C. for 1 day. As the hydrophobizing solution, 20 times the volume of the wet gel was used.
[0137]
(4) Drying process
Finally, the hydrophobized gel was immersed in isopropyl alcohol having a volume 5 times the gel volume and washed twice. Next, the gel was placed in a pressure resistant container, and liquefied carbon dioxide was circulated in the container, whereby isopropyl alcohol in the gel was replaced with liquefied carbon dioxide. Next, the liquefied carbon dioxide was further pumped into the container to raise the pressure in the container to 10 MPa. Then, the inside of a container was made into the supercritical state by heating up to 50 degreeC. Next, drying was completed by slowly releasing the pressure while maintaining the temperature at 50 ° C.
[0138]
(5) Grinding process
The obtained dried gel was pulverized using a blender (manufactured by Walling) to obtain a powder. The average particle diameter of the obtained dry gel powder was 25 μm.
[0139]
The density of the obtained dried gel and the pore volume and specific surface area corresponding to pores of 2 nm to 40 nm were measured. The density was calculated from this value by determining the volume from the weight measurement and the buoyancy when the dried gel was immersed in water. The pore volume and specific surface area were calculated by applying the BJH method and BET method by the nitrogen adsorption method.
[0140]
The processing time of the rebuilding process is 9 hours, 13 hours and 24 hours in order of density (150 kg / m ^Three 250 kg / m ^Three 420 kg / m ^Three ), Pore volume (0.9 cm) ^Three / G, 0.5cm ^Three / G, 0.3cm ^Three / G), specific surface area (390 m ² / G, 270m ² / G, 180m ² / G).
[0141]
(6) Fabrication of molded body
Using a mortar, 100 g of the dried gel powder obtained by the above process, 15 g of fine resin FR-101 (manufactured by Lead City), 200 g of methanol, and 0.2 g of maleic acid are used as binders. And mixed to prepare a slurry-like molding composition.
[0142]
1 part of this composition is poured into a mold having a bottom surface of 3 cm × 3 cm, methanol is evaporated at 50 ° C., dried, and further heated at 120 ° C. for 1 hour, whereby the above methoxymethyl group and amide group A molded body was formed by forming a cross-linkage with a hydrogen atom by a methanol removal reaction.
[0143]
The density of the obtained molded body was calculated from the mass and the volume determined from the shape. The calculated density is 140 kg / m in order of the rebuilding process time of 9 hours, 13 hours, and 24 hours. ^Three 220 kg / m ^Three 360 kg / m ^Three Met.
[0144]
(Comparative Example 1)
For comparison, tetraethoxysilane / ethanol / water = 1/4 (molar ratio) was mixed and gelation was allowed to proceed at room temperature. Water was added and mixed in the form of 0.1N aqueous ammonia. Then, after hydrophobizing and drying like Example 1, it grind | pulverized and the dry gel powder was obtained. However, at the time of drying, in order to suppress the shrinkage of the gel, the solvent in the gel was replaced with hexane instead of isopropyl alcohol, followed by drying. The density of the obtained dry gel powder is 290 kg / m ^Three Met.
[0145]
Using this dry gel powder, a molded product was produced in the same manner as in Example 1. The density of the obtained molded body was 480 kg / m. ^Three Met.
[0146]
Thus, in Example 1, compared with the comparative example 1, even when the density of the used dry gel powder was high, what the density of the molded object was low was obtained. In Comparative Example 1, because of the fine pores of the dry gel powder, gel shrinkage progressed when the solvent that had entered the pores was removed in the drying process, whereas in Example 1, This is probably because the dry gel powder has few fine pores, so that the shrinkage during drying is suppressed.
[0147]
<< Example 2 and Comparative Example 2 >>
In this example, a hydrophobized dry gel, water as a solvent, and a phenol resin as a binder were mixed to prepare a molding composition, and a molded body was prepared using the composition.
[0148]
100 g of dry gel powder produced in Example 1 with a treatment time of the reconstruction process of 24 hours, 30 g of phenolite PG-580 (Dainippon Ink Chemical Co., Ltd.), which is a phenol resin as a binder, and 200 g of water Were mixed using a mortar to prepare a slurry-like molding composition.
[0149]
One part of this composition was poured into a mold having a bottom surface of 3 cm × 3 cm, water was evaporated at 80 ° C. to dry, and further, heating was performed at 150 ° C. for 2 hours to promote crosslinking and form a molded body. .
[0150]
The density of the obtained molded body was 380 kg / m ^Three Met.
[0151]
(Comparative Example 2)
A dry gel powder was obtained in the same manner as in Comparative Example 1 except that a wet gel was prepared using tetraethoxysilane / ethanol / water = 1/3/4 (molar ratio) as the dry gel powder. The density of the dried gel is 210 kg / m ^Three Met.
[0152]
Using the dried gel powder, a molded body was produced in the same manner as in Example 2. The density of the obtained molded body was 620 kg / m. ^Three Met.
[0153]
Thus, in Example 2, although compared with Comparative Example 2, the density of the molded body was low although the density of the used dry gel was high. This is because in Comparative Example 2, when the water having a large surface tension entered the fine pores of the dry gel powder, a larger capillary force was generated, and the shrinkage of the dry gel progressed. In No. 2, it is considered that the shrinkage was suppressed because the dried gel powder had few fine pores.
[0154]
<< Example 3 and Comparative Example 3 >>
In this example, a molding composition was prepared by mixing a dry gel powder having hydrophilicity, an organic solvent, and a binder, and a molded body was prepared using the composition.
[0155]
In the process of Example 1, after performing the process of the reconstruction process for 24 hours, the hydrophobization process was omitted, and the dried gel powder obtained by drying was used in the same manner as in Example 1. Thus, a molded body was obtained.
[0156]
The density of said dry gel powder and a molded object was computed by calculating | requiring a volume from the measurement of mass, and a shape. The density of the dry gel powder is 390 kg / m ^Three The density of the molded body is 360 kg / m ^Three Met.
[0157]
(Comparative Example 3)
A dry gel powder was produced in the same manner as in Comparative Example 2. However, the drying process was carried out by substituting the solvent in the gel with ethanol and naturally drying. The density of the dry gel powder thus obtained is 370 kg / m ^Three Met.
[0158]
100 g of this dry gel powder, 3 g of silicone-based surfactant TSD-4522 (manufactured by Toshiba Silicone) and a surfactant-containing urethane-based emulsion as a binder (manufactured by GENEKA, RU-40-570) as a solid content A slurry-like molding composition was prepared by mixing so as to be 15% of the mass of the powder.
[0159]
Using this composition, a molded body was obtained in the same manner as in Example 3. However, at the time of molding, the molding was carried out by evaporating water at 80 ° C. and drying, and then leaving it to stand at 90 ° C. for 1 day. The density of the obtained molded body was 390 kg / m ^Three Met.
[0160]
Moreover, when the molded body obtained in Example 3 and Comparative Example 3 were overlapped with each other and pressure was applied from both sides, the molded body of Comparative Example 3 was first deformed and cracked. Further, when both molded bodies were immersed in water and dried, the density of the molded body of Example 3 was not changed, but the density of the molded body of Comparative Example 3 was increased by 20% or more.
[0161]
As described above, the strength of the molded body of Example 3 is high because the binder covers the outside of the dry gel powder and the binder penetrates into the pores. In addition to the increase in the strength of the gel powder itself, it is considered that condensation occurs between the hydroxyl group on the surface of the solid skeleton of the dry gel powder and the methylol group of the binder, thereby realizing a strong bond.
[0162]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the molded object containing a dry gel and the manufacturing method of the same improved in intensity | strength than before are provided.
[0163]
The molded body of the present invention has a pore volume of 1 cm in a pore diameter range of 2 nm to 40 nm. ^Three Since a dry gel powder that is less than / g is included, even if a solvent or a binder enters the pores, gel shrinkage or cracking does not occur, so that a molded article having high strength can be obtained.
[0164]
According to the present invention, it is possible to obtain a molded body having a density lower than that of the conventional one, whether using a dry gel powder having hydrophobicity or using a dry gel powder having hydrophilicity.
[0165]
The molded product according to the present invention has a low density and higher strength than the conventional one, and also has excellent solvent resistance during use. Therefore, the molded body according to the present invention is suitably applied to a heat insulating material, an acoustic matching layer, and the like, and has an effect that the restriction of the use environment is greatly relaxed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a method for producing a dry gel according to an embodiment of the present invention.
FIG. 2A is a diagram schematically showing a first solid skeleton in the method for producing a dry gel of an embodiment according to the present invention, and FIG. 2B is a schematic diagram showing a second solid skeleton obtained through a reconstruction process. FIG.
FIGS. 3A to 3E are graphs showing the results of measuring the particle size distribution of particles produced in the reconstructed raw material solution (Example 1). FIGS.
FIG. 4 (a) is a cumulative pore curve (pore volume (cm) determined by BJH method for various dry gels. ^Three / G) and a pore diameter (pore diameter)), and (b) is a differential pore curve.
[Explanation of symbols]
1 First gel raw material solution
2 First wet gel
3 Reconstructed raw material solution (second gel raw material solution)
4 Second wet gel

Claims (7)

A method for producing a molded body containing a dry gel,
  Providing a first gel having a first solid skeleton and first pores;
  Using a gel raw material solution, a restructuring catalyst, and water, reconstructing at least part of the first solid skeleton and forming a second solid skeleton thicker than the first solid skeleton;
  Obtaining a dry gel by drying the gel obtained by the restructuring step;
  The dried gel is pulverized, and the pore volume with a pore diameter in the range of 2 nm to 40 nm is 1 cm. ^Three Preparing a dry gel powder that is less than or equal to / g;
  Preparing a binder composition comprising a binder and a solvent;
  Forming the dry gel powder into a predetermined shape using the binder composition;
Including
  The density of the dry gel powder is 50 kg / m ^Three 500 kg / m or more ^Three The solid skeleton of the dry gel powder is formed from a material containing an oxide of titanium, silicon, vanadium, aluminum, zirconium,
Manufacturing method of a molded object. A molded article comprising the produced dry gel powder and a binder produced by the production method according to claim 1, wherein the pore size of the dry gel powder having a pore diameter in the range of 2 nm to 40 nm is 1 cm. ^Three / G or less, and the density of the dry gel powder is 50 kg / m ^Three 500 kg / m or more ^Three A molded article, wherein the solid skeleton of the dry gel powder is formed from a material containing oxides of titanium, silicon, vanadium, aluminum, and zirconium. The manufacturing method of the molded object of Claim 1 in which the said binder has penetrate | invaded the inside of the pore of the said dry gel powder. Comprising the step of entering said binder pores of the dry gel powder, method for producing a molded article according to claim 1. The method for producing a molded body according to claim 1 or 4 , wherein the dry gel powder has hydrophobicity and the solvent is an organic solvent. The method for producing a molded article according to claim 1 or 4 , wherein the dry gel powder has hydrophilicity. 5. The method for producing a molded article according to claim 1, wherein a reconstruction catalyst used in the reconstruction step is an organic acid, an inorganic acid, an organic base, or an inorganic base.

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